In recent years, a number of proposals have been made to enable a motor vehicle to automatically track a driving lane. There are two known major control principles.
(1) The vehicle is equipped with a video camera, typically consisting of a CCD camera, which gathers information on the current position of the vehicle, and sensors for detecting certain dynamic state variables of the vehicle. The changes in the curvature of the road path are treated as unknown disturbances. The vehicle follows the driving lane by receiving information on the deviation of the vehicle position from the center of the driving lane and the dynamic state variables of the vehicle as a feedback signal. Refer, for instance, to "Automatic Path Tracking Using Linear Quadratic Control Theory--Control Method for a Curved Path", by H. Furusho and H. Mouri, Proceedings of JSAE Semi-Annual Convention, No.972, May 1997, pp. 49-52. PA1 (2) The vehicle is equipped with a video camera which gathers information on the road path lying ahead of the vehicle, and sensors for detecting certain dynamic state variables of the vehicle. A preview control based on the predicted course of the road path is carried out in combination with the feedback control based on the dynamic state variables of the vehicle. Refer, for instance, to "Preview Control for Vehicle Lateral Guidance in Highway Automation", by H. Peng and M. Tomizuka, ASME Journal of Dynamic Systems, Measurement and Control, December 1993, Vol. 115, pp. 679-686.
According to the first principle (1), because the control process relies on the current course information, there is some difficulty in achieving an optimum selection of control parameters for successfully tracking the curved path of the road, and a somewhat excessive time delay or overshoot is inevitable. In the case of the second principle (2), a smooth tracking of the course of the road may be possible, but the state variables for the feedback control include those which cannot be measured directly, and the high-speed estimation of such state variables requires a high speed computing unit. Therefore, the system tends to be unacceptably complex and expensive.